The invention relates generally to heat seal devices and more particularly to impulse heat seal devices.
Flexible packaging products are used to protect a wide variety of articles from both physical abuse and contamination. These packaging products include, for example, plastic bags or pouches that can be useful for packaging items such as food, and cushion materials such as air cellular material.
Flexible packaging can be prepared from sheets of laminates or films that are bonded together to form a desired product. The packaging may include thermoplastic materials that can be bonded together using a heat seal. A heat seal is produced by applying heat to the thermoplastic materials until they melt together and effectively fuse to form a seal. In many circumstances it may be desirable to bond two sheets of thermoplastic material together to form a continuous running seal. It may be difficult to use heat to fuse unsupported materials together to form a continuous running seal because the materials may melt and stick to the heating element or the seal may separate when it is no longer supported by the heating element.
One technique for producing a continuous running seal includes passing the thermoplastic materials that are to be fused together over a heated drum. Typically, the entire surface of the drum is heated via an interior resistor wire or hot fluid. As the materials pass over the surface of the drum, the heat fuses the films together. If the newly sealed films leave the drum still heated, the seal will not have cooled sufficiently to produce a strong bond and the seal can separate or tear. As a result, these devices typically require the presence of a Teflon belt between the films and the drum. The Teflon belt prevents the film from adhering to the drum and provides additional support for the newly formed seal after it has left the drum.
In another technique, a continuous seal can be made by passing the thermoplastic materials between heated rollers. A disadvantage associated with this method is that the dwell time for heat sealing between the rollers is extremely short. Typically, good seals can be made only if the rollers are moving very slowly or if the materials are preheated before passing through the heated rollers. Additionally, the newly formed seal may tear or rupture if the fused materials are not adequately supported after passing between the rollers.
Impulse sealing is another commonly used method to produce a continuous seal. In one form of impulse sealing, the materials are indexed forward between opposed sealing jaws. An electrically resistive material, such as nichrome resistive wire is positioned within one of the jaws and covered with an electrically insulating layer. The thermoplastic materials are indexed forward between the jaws and an electric current is passed through the resistive wire to fuse the materials. After the current turns off, the transfer of heat from the thermoplastic materials to the jaws facilitates faster cooling and solidification of the newly formed seal. The jaws are then opened and the fused materials are indexed forward to produce the next seal. The advantage of this method is that the seal is cooled to achieve adequate strength before the jaws are opened. The disadvantage of this system is that it requires more time and the materials cannot be continuously moved forward in a seamless manner.
Thus, there still exists a need to provide a device and method for producing a continuous heat seal in heat sealable materials that provides adequate heating for producing the seal while at the same time supporting the newly formed seal until it is adequately cooled.